1. Technical Field
This invention relates generally to filtration, and more particularly to a method and filter element for filtering contaminants from internal combustion and industrial engine oil.
2. Description of Related Art
Recall that a typical full flow filter system in an on-highway truck application allows a flow rate in the range of about twenty to forty gallons per minute. Passing oil at that flow rate through a pleated paper, stacked disc, or other conventional filter element filters particulate matter down to about 40 microns in size from the engine oil. But it often fails to effectively trap smaller particles and remove moisture, and so the oil must be changed more frequently than desired.
Truck owners often use an auxiliary bypass filter for additional filtering. A typical bypass filter retrofits to the truck engine where it diverts oil through a finer auxiliary filter element at a much slower rate (e.g., 2.5 gallons per minute or less). Passing the oil through the auxiliary filter element helps filter out particles smaller than 40 microns. That improves engine oil life and the life of the engine.
But existing bypass filters have certain problems that need to be overcome. For example, many existing bypass filter elements are surface filters in the sense that filtering occurs at just the outer surface of the element where the oil first enters the element. With very fine surface filter elements, particles tend to accumulate at the outer surface, thereby loading the filter element and cutting off the flow of liquid through it. As a result, filtering is degraded and the element must be changed more frequently than desired. So, owners need a way to filter engine oil that alleviates the foregoing surface buildup problem.
In addition, many existing bypass filter elements result in "channeling" in the sense that the oil passes through the filter element along one or more channels or paths of less resistance. The filter element may initially have such paths of less resistance (a problem in rolled media filters made with cotton/synthetic fibers composition) or develop them over time (a problem of filters packed with cotton/synthetic fibers, sawdust, hulls, and other such media). Oil passing under pressure through the filter element seeks out the channels, and a breach in the surface of the filter element may even allow the oil to flow through the filter without any filtering at all. Thus, owners need a way to filter engine oil that also alleviates the foregoing channeling problem.